1. Field of the Invention
This invention relates to an electronic measuring device capable of indicating a measured value in the form of both analogue and digital displays.
2. Description of the Prior Art
So-called mechanical analogue gauges of the type in which the linear movement of a spindle is converted into the rotational movement of a pointer through the medium of a motion conversion mechanism formed by a rack, pinion, etc., and/or an enlarging mechanism formed by gears including a sector gear and in which the pointer indicates a graduation on a scale to be read as a measured value have been traditionally used in various fields.
Lately, so-called electronic dial gauges such as the sort which incorporates in the main body an encoder operated in accordance with the movement of a spindle and which indicates a measured value obtained by the encoder in a digital display effected by a digital indicator are being used increasingly.
In general, these electronic dial gauges, which are disadvantageous in economic terms, are adopted for the reason that they have properties of high resolution and high accuracy and are easy-to-read, while mechanical dial gauges are adopted in consideration of their capability to operate without any power source as well as their easy-to-use properties, when the degree of accuracy required is not more than their rated accuracy. Also the latter type are more likely to be adopted in circumstances where it is necessary to determine for acceptance or rejection whether articles being measured fall within a predetermined range of value.
However, in practice, it is not possible to carry out measurement by employing only one of these two types of devices, because the kind of object to be measured, the mode of measurement, and matters of skill and tradition or the like must be considered. Thus, it has been generally necessary to provide both types.
When one of these types of device is employed for measurement, it is often found that the characteristic of the other type is required. For instance, in the case of a mechanical dial gauge which is employed in order to decide, for acceptance or rejection, whether articles fall within a certain range, it is often desirable to know by what amount rejected articles fall short of the predetermined value. On the other hand, in some cases, it is not always necessary to constantly read a digital display which changes every moment as it may be sufficient simply to judge the intermediate tendency thereof.
This situation may result in the idea of combination of the two different types, but it is difficult for an arrangement which consists solely of a simple combination to define a desirable relationship between the values read from different types of displays. Such a simple combination would merely complicate the structure and increase the cost.
In particular, when the graduations of an analogue display are designed to correspond to the minimum place unit of the digital display, the pointer must make several tens or hundreds of turns. If a spindle stroke of 100 .mu.m is assumed to correspond to one revolution of the pointer, the pointer makes a hundred revolutions for a spindle stroke of 10 mm. Such a large number of revolutions is a burden on the mechanism of the pointer and it may damage the same.
If the device is designed to allow both the read values to correspond to each other, it is possible to read it on the digital display with a high resolution over a wide range and it is not difficult on the analogue display. For this reason, the device is so arranged that the range which can be read by means of the graduations and the pointer corresponds to two or three places on the digital display. However, it is impossible for this arrangement to indicate a value in the analogue form with respect to objects to be measured which are outside the range readable with the graduations and the pointer.